The primary goal of the proposed research is to investigate the pathogenesis and epidemiology of enteropathogenic Escherichia coli (EPEC) using molecular genetic techniques. Enteropathogenic E. coli have been defined as diarrheagenic E. coli which do not elaborate heat-labile (LT) or heat-stable (ST) enterotoxins, do not invade the intestinal mucosa and belong to certain "classical" serotypes epidemiologically incriminated to be associated with infantile diarrhea. EPEC have been shown to be important causes of infantile gastroenteritis in both industrialized and developing countries. Although the exact pathogenic mechanisms of this organism are not known, recent experimental and clinical evidence indicates that adhesion of the bacterium to the intestinal mucosa is an essential step. An in vitro adhesion assay employing cultured HEp-2 cells has been described for these strains and two distinct morphologies of adherence (diffuse and localized) have been recognized. We have identified plasmids which code for the ability of the EPEC to adhere to HEp-2 cells in both morphologies and have already shown that the plasmid conferring localized adherence correlates with the ability of the parent strain to cause human diarrhea. The genes encoding both types of adherence will be cloned and specific mutants prepared to assess the importance of these factors in diarrhea. Using the cloned genes, DNA probes will be developed to diagnose EPEC in pure cultures and in stool specimens. The probes will allow us to better study the epidemiology of EPEC and to determine the epidemiologic importance of HEp-2 adhesins.